As shown in FIGS. 7(a), 7(b), 7(c), 7(d) and 7(e), a small-sized stepping motor which is used in a digital camera, a digital video camera, a slim ODD or the like commonly includes a case 2′ within which a rotor and a coil are disposed, a pivot bearing 82′ which receives the axial end of a rotor shaft of the rotor on one end side of this case 2′, and a bearing holder 81′ provided with a through hole 810′ into which the pivot bearing 82′ is inserted. Further, a spring member 80′ provided with a flat spring part 83′, which urges the pivot bearing 82′ in the through hole 810′ to the axial end of the rotor shaft, is disposed on a further end side of the bearing holder 81′ (see, for example, Japanese Patent Laid-Open No. 2003-324892).
In the stepping motor constructed as described above, the case 2′ is commonly formed in a circular cylindrical shape when the case is cut in a direction perpendicular to the axial line of the motor. Alternatively, as shown in FIGS. 7(a) and 7(b), the case of some motors may be formed in an elliptical cross-section in order that the thickness dimension of the motor in a direction perpendicular to the axial line of the motor, i.e., in the radial direction of the motor is made smaller. In any case, the spring member 80′ is required to be mounted to the bearing holder 81′. Therefore, conventionally, four engaging pawl parts 801′, 802′, 803′, 804′ are formed in the spring member 80′ so as to engage with the bearing holder 81′ through a substantially central portion of the outer peripheral side face of the bearing holder 81′.
In such a stepping motor, it is required that the thickness dimension in a direction perpendicular to the axial line of a motor, for example, the dimension “A′” is further made smaller and thus the engaging portion of the spring member 80′ with the bearing holder 81′ is also required to be made smaller. However, since the through hole 810′ into which the pivot bearing 82′ is inserted is formed in the bearing holder 81′, the wall thickness “t′” of the periphery of the through hole 810′ is required to be made too thin when portions 811′, 812′, 813′, 814′ (see FIGS. 7(d) and 7(e)), with which the engaging pawl parts 801′, 802′, 803′, 804′ of the spring member 80′ engage, are made thinner in the bearing holder 81′. Therefore, the accuracy of the dimension and shape of the through hole 810′ is significantly reduced.
Further, it is conceivable that the number of the engaging portions is reduced to two portions from four but, in this case, a fixing force is reduced and thus shock resistance is lowered. In addition, the engagement with two portions is capable of positioning in only one direction and thus another positioning mechanism is required to be added for positioning in another direction.
Further, it is conceivable that the spring member 80′ is formed to be even thinner. However, in this case, the strength of the spring member 80′ is reduced and the spring force of a flat spring portion becomes unstable.